Retrieving hydrocarbons from subterranean reservoirs is becoming more difficult, as existing reserves are depleted and production becomes more expensive. It has been estimated that mature fields account for up to 70% of the world's production or more. In order to increase production, reservoirs are often hydraulically fractured to stimulate production of hydrocarbons from the wellbore. Hydraulic fractures are created in subterranean formations by hydraulically injecting water or high viscosity fluid (also referred to as fracturing fluid) containing a proppant at a high flow rate into a wellbore and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack, creating or enlarging one or more fractures. The proppant subsequently prevents the fracture from closing completely and thus provides improved flow of recoverable fluid, i.e., oil, gas or water.
Because aging wells are often produced from multiple intervals, some very thin, the ability to locate these stimulation treatments with pinpoint accuracy is key to more effective remediation and increased ultimate recovery. An accurate method of visualizing fracture length, proppant penetration, and estimated flow in the created fracture are required to precisely access production capabilities and the need for further remediation before production is initiated.
Numerous techniques exist for detecting the fracture geometry of a well using various imaging techniques. For example, Hocking et al., U.S. Pat. No. 6,330,914 provides a method for monitoring a propagating vertical fracture in a formation by injecting conductive fracture fluid into the formation to initiate and propagate the fracture; energizing the fracture fluid while the fracture propagates; and measuring the inducted electromagnetic field parameters to judge the fracture development and geometry. Further, McCarthy, et al., WO2007013883, introduces a target proppant; transmits electromagnetic radiation from about 300 megahertz-100 gigahertz; and analyzes a reflected signal from the target particle to determine fracture geometry. Lastly, Nguyen et al., U.S. Pat. No. 7,073,581, describes an electroconductive proppant composition and related methods of obtaining data from a portion of a subterranean formation. All of these techniques focus on detecting data utilizing coated proppants and electrical currents applied in a bore hole setting.
These and other conventional techniques for detecting fracture geometry fail to account for how the data in the field is actually measured. These techniques are generally single sensor based approaches, which either measure the information in the borehole or between boreholes. On the surface, these techniques use a single sensor and move the sensor back and forth in a grid like fashion around the surface with an individual receiver and individually recorded data is utilized to make a map of the results. This map can then be used to model or infer the size and nature of the fracture body.
One of the critical flaws in this approach is the significant time required to make all of these individual measurements. Additionally, it is common for the field being measured to change over time due to earth effects, like the changing magnetic field, sunspots, and movement of man and equipment on the surface.
Knowing, measuring, and translating data from various sensors and tools is of prime importance to the completion engineer in order to determine if fracturing was successful and as a predictor of expected production rates from the well. It is therefore an object of the present invention to provide a method and apparatus for evaluating the geometry of a fracture.